Fastening systems based on pressure sensitive tape constructions are finding increasing utility in numerous applications, as alternatives to mechanical fastening techniques. For example, such tape constructions are used for the attachment of various components, including film graphics, body side molding, body sealing weatherstripping, and most recently, for glass installation. In addition to the automotive industry, there exists many other applications/markets for attachment tapes of this type.
PSA coated tapes based on acrylics, neoprene, polyolefins, polyurethanes, silicones and rubber resin-based materials are currently in use, and provide a generally desirable balance of properties for many purposes. However, more demanding applications, such as those in the automotive industry, require materials with a balance of properties not yet available in commercial products. For example, newer automotive paint systems are formulated for enhanced environmental conservation, appearance, durability, and resistance to degradation from common sources of contamination. These formulation changes have also made the paint substrates more difficult to adhere to for conventional PSAs.
In addition, new or potential applications require ever higher performance in tests such as peel adhesion and resistance to shock/impact at low temperatures (-30 to -45.degree. C.). Conventional acrylic-based PSAs lack the desired adhesion and low temperature impact resistance when mounted on these new substrates.
Traditional silicone pressure sensitive adhesives, which by nature exhibit excellent low temperature shock resistance properties, do not generate adequate adhesion to these paints, apparently due to lack of strong interaction with the paint surface. Thus, there exists the need to design new PSAs which possess the required balance of properties.
Attempts have been made to provide "hybrid" systems having the advantages of acrylate PSAs and silicone PSAs, but the approach generally taken has been to blend the two types of PSAs. Thus, these hybrids are prone to gross phase separation problems and their properties are also somewhat limited. In addition, the systems are solvent-based or water-based, necessitating a drying step.
For example, European Patent Publication No. 289928 (General Electric), published Nov. 9, 1988, describes an emulsion or solution comprising: (a) 100 parts by weight of water or organic solvent; (b) from about 10 to about 400 parts by weight of pressure sensitive adhesive comprising: (i) from about 50 to about 99% by weight organic pressure sensitive adhesive, preferably an acrylate, and (ii) from about 1 to about 50% by weight of silicone pressure sensitive adhesive; and (c) an effective amount of organic peroxide or alkoxy silane cross-linking agent to increase the shear strength of the composite adhesive through crosslinking of the silicone. The emulsion generally requires the use of an emulsifying agent or agents to maintain both the micelles of silicone adhesive and micelles of organic adhesive in a substantially stable state of suspension even at low water content, so that drying may be accomplished prior to phase separation of the silicone adhesive and the organic adhesive.
Similarly, U.S. Pat. No. 4,791,163 (Traver et al.) discloses an emulsion (formed from a silicone PSA and an organic PSA, preferably an acrylate) comprising: (a) 100 parts by weight of a continuous phase of water; (b) from about 10 to about 400 parts by weight of micelles comprising: (i) from about 50 to about 99% by weight of micelles comprising organic pressure sensitive adhesive, preferably an acrylate, and (ii) from about 1 to about 50% by weight of micelles comprising silicone pressure sensitive adhesive; and (c) an amount of emulsifying agent effective to maintain the emulsion. Curing of the silicone may be promoted by adding a peroxide or by adding a catalyst and an alkoxy silane.
Japanese Patent Publication No. 62-295982 (Toyota Gosei), published Dec. 23, 1987, describes organic solvent-based blends of silicone pressure sensitive adhesive, active hydrogen containing acrylic pressure sensitive adhesive, and polyurethane and/or polyisocyanate.
Japanese Patent Publication No. 60-197780 (Daicel), published Oct. 7, 1985, also discloses blends in organic solvent of 100 parts by weight acrylic pressure sensitive adhesive and 1-30 parts by weight silicone pressure sensitive adhesive.
Japanese Patent Publication 61-57355 discloses solvent based adhesives having a silicone pressure sensitive adhesive, an acrylate pressure sensitive adhesive, and an organic peroxide crosslinking agent to prevent phase separation. The adhesives mentioned are solvent based adhesives.
Japanese Patent Publication Nos. 59-145269 (Nitto), published Aug. 20, 1984, and 63-291971 (Nitto), published Nov. 29, 1988, seek to avoid the gross phase separation problems characteristic of blends through the use of either bridging agents or compatibilizing agents. The former patent describes a composition comprising a medium, 100 parts by weight of acrylic adhesive polymer dissolved or dispersed in the medium, 5-120 parts by weight silicone adhesive polymer, and crosslinking agent capable of co-bridging both polymers. The latter patent discloses pressure sensitive adhesives comprising silicone pressure sensitive adhesive, polyacrylate pressure sensitive adhesive, and silicone polyacrylate graft copolymer.
These adhesives have been used for various automotive applications, e.g., attachment of decorative items to the painted surface. Automotive industry testing of adhesives typically subjects adhesives to pass a shock test, known in the industry as a "cold slam" test, at temperatures down to -45.degree. C. Conventional acrylate adhesives have difficulty passing such tests when attached to new high solids paints systems which are increasingly used in the automotive industry. Adhesion to such paints is also reduced as compared to older paints.
Additional patents disclose ultraviolet radiation curing of acrylate adhesives. U.S. Pat. No. 4,364,972 (Moon) discloses the use of N-vinyl-2-pyrrolidone as the polar copolymerizable monomer in the acrylate adhesive copolymer. High adhesion to automotive paints is disclosed but not exemplified.
A need exits for a PSA and a PSA coated tape having superior adhesion to paint and superior low temperature shock resistance properties. A need also exists for a hybrid PSA system and a paint-adherable tape coated with a hybrid PSA system which has the advantages of both acrylate PSAs and silicone PSAs which requires little or no solvent, thereby reducing or eliminating the environmental and health hazards associated with solvent use, as well as the need for drying. A need also exists for such a hybrid PSA system paint-adherable tape coated with a hybrid PSA system which is radiation curable and which, unlike most known hybrid systems, is not prone to gross phase separation problems. A need also exists for a hybrid PSA system and a paint-adherable tape coated with a hybrid PSA system which possesses balanced PSA properties tailorable over a wide range, thereby providing greater flexibility than known hybrid systems in achieving substrate-specific adhesion. We have discovered such a PSA and such a PSA coated tape.